URL not supported by this version

Cause:

This error appears

Example:

A HTML with a custom DTD:

Good<!DOCTYPE html PUBLIC "-//example.com//DTD XHTML 1.1 plus MyData 1.0//EN" "http://www.example.com/DTD/xhtml11-my_data.dtd">
Good<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

Solution:

Check that the DTD that you use exists and is one of the official W3C DTDs. If you need special tags, use XML and XSLT, not XHTML.

References: